This invention relates to a rotatable abrading device, and more particularly, to a mechanical device for propelling abrasive materials at abrading velocities against a surface to be treated. Such devices are commonly known as abrasive throwing wheels or centrifugal blasting machines. This invention also relates to an abrasive throwing blade and to an assembly comprised of the blade in position on the abrasive throwing wheel.
Centrifugal blasting machines comprising rotors or wheels having a plurality of blades installed thereon have been known in the art for many years. When the wheel is rotated at very high speeds, the blades propel an abrasive material against a work surface. The blades are sometimes referred to as abrasive throwing blades or simply throwing blades. Due to the action of the abrasive material on the throwing blades, the blades exhibit considerable wear over a period of time. Attempts have been made to fabricate the throwing blades from abrasion resistant alloys. In other cases, special blade configurations have been employed to minimize the effects of the abrasive material on the blades.
Notwithstanding these attempts to minimize wear and extend the life of the throwing blades, periodic blade removal and replacement cannot be avoided. This results in a loss of valuable operating time. Furthermore, while the blades must be removable, they must also be held securely in place such that they resist the tremendous centrifugal and other forces exerted on them when the abrasive throwing wheel is rotated at high speeds.
Several methods have been proposed for securing the throwing blades in a removable manner to the throwing wheel. One method involves securing the blades to the front side of a wheel disk, usually by means of a bolt or by means of radial grooves in the wheel, frequently of a dove tail shape. Another method employs two wheel disks that are maintained in spaced-apart relation. Longitudinal narrow edges of the throwing blades are generally inserted into radial grooves arranged in opposing surfaces of the two disks. Auxiliary means, such as bolts, pivotal locking means, eccentrics, set screws, etc. can be employed to secure the blades against radial displacement. Examples of these devices can be found in U.S. Pat. Nos. 2,819,562, 3,352,064, and 3,654,736. Blade replacement in these designs is not always easy because a number of parts must be disassembled to access the blade or because the blades may xe2x80x9cfreezexe2x80x9d or become jammed in the grooves in the wheel.
A number of other designs have been proposed. For example, U.S. Pat. No. 2,696,364 describes a turbine mounted on a shaft and a plurality of buckets mounted between an inner plate and an outer plate. The buckets are held between the plates by machine bolts, which pass completely through the wheel perpendicular to the plane of the wheel. The bolts clamp the plates and grip the turbine buckets between teeth formed on roots of the buckets and on peripheral marginal faces of the plates.
U.S. Pat. No. 2,955,799 describes a rotor including a hub and a plurality of blades circumferentially spaced about the hub. Interengaging means mount the blades in the hub with axial play therebetween. The blades have roots, and the interengaging means include a single pin support connecting the root of each blade to the rotor.
U.S. Pat. No. 2,970,809 relates to a rotor structure having a rim portion with a recess that receives a radially extending blade. The blade has a root portion of less thickness than the width of the recess. Thus, the blade is loosely received in the recess. A pin is provided for insertion in the rim and through the root portion for supporting the blade.
U.S. Pat. No.3,165,294 relates to a rotor drum provided with a plurality of axially spaced, circumferentially extending slots of dovetail shape. A loading recess is provided in the radially inward wall of the dovetail slot. A radially extending threaded or tapped hole is provided adjacent the loading recess, a threaded member of plug being received therein. The head of the threaded plug is provided with a recess for receiving a tool, such as an Allen wrench, for screwing the threaded plug into and out of the tapped hole.
U.S. Pat. No. 3,287,858 describes a blasting wheel, which supports in vane channels a vane secured to a steel backing plate, which is, in turn, anchored to a channel in the wheel by bolts in a block that is integral with the plate or secured thereto. A positioning pin is used to position the backing plate in the vane channel. The vane face also is connected with the backing plate by a pin that seats in an opening in the backing plate. The pin serves as a positioning element and a reinforcement against centrifugal force developed during operation of the wheel. The pin connection prevents the plate and vane from sliding axially following development of centrifugal force.
U.S. Pat. No. 3,368,308 relates to a throwing wheel and a shaft rotatably mounted on suitable journals and carrying a runner head upon which throwing blades are mounted. The blades are equally spaced around the runner head and can be held in any suitable manner, such as by use of an enlarged dove tailed edge on one side of the blade engaging a corresponding dove tailed slot in the face of the runner head.
U.S. Pat. No. 3,867,791 describes a throwing blade that is secured to a wheel by means of a blade block, which is mounted on the wheel. The blade block has a first groove near an inner end of the block and a second groove near an outer end. The blade includes lugs for insertion in the grooves. A centrally disposed impeller restricts movement of the blades, particularly in a radial direction. The blades are thus maintained in a fixed position on the blade blocks. While commercial success has been achieved with this device, the rear of the blade must generally be machined in the area where it contacts the impeller. This adds to the cost of the blade. Additionally, it is rather difficult to cast a blade of the type disclosed in the patent because of its large cross-sectional area.
Another arrangement is shown in U.S. Pat. No. 3,894,360. In this design, the blades are mounted on brackets having an angular cross-section, and the brackets, in turn, are mounted on the throwing wheel. The rear of each blade is provided with a cast-in insert stud, which is adapted for insertion through an opening in the angular bracket. The stud is provided with a slot adapted to receive a clip, which holds the blade in position on the angular bracket. The only securing means in this arrangement is comprised of the stud and the spring clip. Should either the stud or spring clip fail, such as by wear around the area of the stud, the blade may fly off the wheel.
U.S. Pat. No. 4,249,350 provides, in combination, a blade block adapted for mounting on an abrasive throwing wheel and a blade supported by and detachably connected to the blade block. The blade has an inner end, an outer end, a forward surface and a rear surface. Cooperating engagement means are provided on the blade block and the blade for permitting inward movement of the blade while preventing substantial outward movement thereof relative to the blade block. An abutment means on the blade block acts as a bearing or driving surface for the blade. The abutment surface is located outwardly of the engagement means and usually contacts the rear surface of the blade. The abutment means substantially prevents rearward movement of the blade without obstructing its forward movement. Locking means substantially prevents inward movement of the blade relative to the blade block in order to prevent disengagement of the cooperating engagement means.
U.S. Pat. No. 4,649,673 describes a shot blasting wheel having a base plate with angularly spaced, elongated grooves that engage complementary tongue formations on throwing blades. A rearwardly directed lug is provided on each blade, which is engaged by a bolt or stud, which is parallel to the surface of the blade and enters the wheel normal to the plane of the wheel. The lug includes a wedging surface, which results in a force on the lug to lock the tongue formation in the groove. The interengaged tongue and groove are shielded against the ingress of shot.
U.S. Pat. No. 5,074,754 describes a rotor blade, which is releasably connected to a closed-sided retention member. The retention member is releasably affixed to a rotatable hub. A shaped root of the rotor blade is retained within the closed-sided retention member by a shaped flange and a shaped retention plate. The shaped root of the rotor blade is secured within the retention member without a direct bolted connection.
U.S. Pat. No. 5,081,801 relates to a blast wheel provided with a plurality of blades having generally an xe2x80x9cIxe2x80x9d shape in cross-section, each blade includes a base having a hooking member at one end for anchoring with the wheel. The opposite end of the blade from the hooking member is provided with a lug extending downwardly from the bottom surface for anchoring in the wheel after engagement of the hooking member with the wheel. The lug also extends outwardly from the end of the blade forming a bearing surface substantially co-planar with, but opposed in direction to, the bottom surface of the blade. The hooking member is inserted into the peripheral recesses of the wheel for anchoring therewith, thereby restricting axial, circumferential, and radial inward movement of the outward end of the blade.
U.S. Pat. No. 5,209,024 relates to an abrasive blast wheel comprising a combination of a hub, radially extending blades, and an impeller plate for a blast wheel. Each of the blades includes an anchoring base of a transverse width greater than a remainder of the blade. The impeller plate has a plurality of radial slots, one radial slot for each of the blades. The impeller plate is axially secured relative to the hub to axially clamp the blade bases to the hub with the blades being retained against radial outward movement by the blade anchoring base end engaging the hub flange.
U.S. Pat. No. 5,462,411 describes a blade-hub connection using an element in the shape of an xe2x80x9cLxe2x80x9d, which is inserted into a cavity of a blade. One of the legs of the L-shaped element is substantially aligned on the longitudinal axis of the blade itself. A second, shorter leg of the L-shaped element is placed perpendicular to the plane of the blade and adapted for placement in a position parallel to the plane of the hub. A hole is made to allow for the passage of a screw, which bolts the blade attachment to the hub by passage into the hub perpendicular to the plane of the hub.
U.S. Pat. No. 5,476,412 relates to a blade for mounting on a centrifugal blasting wheel without using a separate stop member to prevent outward radial movement of the blade.
The blade replacement designs just described have several features in common. They require multiple elements for fastening the throwing blade to the abrasive throwing wheel. These elements include, for example, blade blocks, blade locking plates, and retainer clips. These designs also have special shaping and forming requirements for the throwing blades and the abrasive throwing wheel. For example, in some cases the blades must be formed with recesses and apertures for mating with corresponding elements on the abrasive throwing wheel or auxiliary parts.
Thus, notwithstanding the numerous designs for replacement of throwing blades on abrasive throwing wheels, there still exists a need in the art for improved means for securing the throwing blades to the abrasive throwing wheel of a centrifugal blasting machine. The throwing blades must be securely mounted on the wheel to prevent movement of the blades, especially in a radial direction following the development of centrifugal force by rotation of the wheel. The blades should be easily removed and replaced without the need for special tools. Preferably, the blade should not be susceptible to xe2x80x9cfreezingxe2x80x9d0 or jamming in position, as is frequently encountered when the blades are installed in grooves on a face of the wheel. When the wheel and blade assembly is installed in a centrifugal blasting machine, it should be possible to replace the blade without removing internal parts, such as the impeller and control cage, conventionally found in such machines. The design should dispense with the need for adhesive materials that temporarily hold blades in position during assembly. The design should also dispense with the need for retaining clips and similar small fasteners that are difficult to handle and manipulate. The assembly should not require machining and close tolerances characteristic of some prior art devices. The means used for locking the blade in position should be suitable for use with any length and width of blade. For commercial reasons, the wheel and blade assembly should be adapted to fit centrifugal blasting machines now in use.
This invention aids in fulfilling these needs in the art by providing a blast wheel assembly comprising an abrasive throwing wheel and a plurality of throwing blades evenly spaced axially on the wheel. The wheel has a central opening, an outer periphery, and a plurality of channels therein for receipt of the throwing blades. The channels extend from the outer periphery with a diminishing cross-section toward the central opening. The outer periphery includes an opening for insertion of a fastener. Each of the blades comprises an inner end, outer end, a surface for throwing abrasive, and a bottom surface substantially perpendicular to the abrasive throwing surface. Each blade diminishes in cross-section from its outer end to its inner end. Each blade includes a lug disposed proximate the outer end and between the outer end and the inner end of the blade. The lug has an opening therein adapted to align with the opening in the outer periphery of the wheel when the blade is inserted in one of the channels in the wheel. Each channel and the bottom of each blade are of complementary dove tail shape so that the channel slidably receives the blade and engages the blade to securely position the blade in the channel.